## 339. Nested List Weight Sum

Given a nested list of integers, return the sum of all integers in the list weighted by their depth.

Each element is either an integer, or a list -- whose elements may also be integers or other lists.

Example 1:

``````Input:
[[1,1],2,[1,1]]
Output:
10
Explanation:
Four 1's at depth 2, one 2 at depth 1.
``````

Example 2:

``````Input:
[1,[4,[6]]]
Output:
27
Explanation:
One 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 4*2 + 6*3 = 27.
``````
``````/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* public interface NestedInteger {
*     // Constructor initializes an empty nested list.
*     public NestedInteger();
*
*     // Constructor initializes a single integer.
*     public NestedInteger(int value);
*
*     // @return true if this NestedInteger holds a single integer, rather than a nested list.
*     public boolean isInteger();
*
*     // @return the single integer that this NestedInteger holds, if it holds a single integer
*     // Return null if this NestedInteger holds a nested list
*     public Integer getInteger();
*
*     // Set this NestedInteger to hold a single integer.
*     public void setInteger(int value);
*
*     // Set this NestedInteger to hold a nested list and adds a nested integer to it.
*
*     // @return the nested list that this NestedInteger holds, if it holds a nested list
*     // Return null if this NestedInteger holds a single integer
*     public List<NestedInteger> getList();
* }
*/
class Solution {
public int depthSum(List<NestedInteger> nestedList) {
return dfs(nestedList, 1);
}
private int dfs(List<NestedInteger> nestedList, int depth){
int sum = 0;
for(NestedInteger ni: nestedList){
if(ni.isInteger()) sum+= ni.getInteger() * depth;
else sum+= dfs(ni.getList(), depth + 1);
}
return sum;
}
}
``````